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.TH MQ_SEND 3C "Oct 23, 2014"
.SH NAME
mq_send, mq_timedsend, mq_reltimedsend_np \- send a message to a message queue
.SH SYNOPSIS
.LP
.nf
#include <mqueue.h>

\fBint\fR \fBmq_send\fR(\fBmqd_t\fR \fImqdes\fR, \fBconst char *\fR\fImsg_ptr\fR, \fBsize_t\fR \fImsg_len\fR,
     \fBunsigned\fR \fImsg_prio\fR);
.fi

.LP
.nf
#include <mqueue.h>
#include <time.h>

\fBint\fR \fBmq_timedsend\fR(\fBmqd_t\fR \fImqdes\fR, \fBconst char *\fR\fImsg_ptr\fR,
     \fBsize_t\fR \fImsg_len\fR, \fBunsigned\fR \fImsg_prio\fR,
     \fBconst struct timespec *restrict\fR \fIabs_timeout\fR);
.fi

.LP
.nf
\fBint\fR \fBmq_reltimedsend_np\fR(\fBmqd_t\fR \fImqdes\fR, \fBconst char *\fR\fImsg_ptr\fR,
     \fBsize_t\fR \fImsg_len\fR, \fBunsigned\fR \fImsg_prio\fR,
     \fBconst struct timespec *restrict\fR \fIrel_timeout\fR);
.fi

.SH DESCRIPTION
.LP
The \fBmq_send()\fR function adds the message pointed to by the argument
\fImsg_ptr\fR to the message queue specified by \fImqdes\fR. The \fImsg_len\fR
argument specifies the length of the message in bytes pointed to by
\fImsg_ptr\fR. The value of \fImsg_len\fR is less than or equal to the
\fImq_msgsize\fR attribute of the message queue, or \fBmq_send()\fR fails.
.sp
.LP
If the specified message queue is not full, \fBmq_send()\fR behaves as
if the message is inserted into the message queue at the position
indicated by the \fImsg_prio\fR argument. A message with a larger
numeric value of \fImsg_prio\fR is inserted before messages with lower
values of \fImsg_prio\fR.  A message will be inserted after other
messages in the queue, if any, with equal \fImsg_prio\fR. The value of
\fImsg_prio\fR must range from zero to \fBMQ_PRIO_MAX - 1\fR.
.sp
.LP
If the specified message queue is full and \fBO_NONBLOCK\fR is not set in the
message queue description associated with \fImqdes\fR (see \fBmq_open\fR(3C)
and \fBmq_setattr\fR(3C)), \fBmq_send()\fR blocks until space becomes available
to enqueue the message, or until \fBmq_send()\fR is interrupted by a signal. If
more than one thread is waiting to send when space becomes available in the
message queue, then the thread of the highest priority which has been waiting
the longest is unblocked to send its message. Otherwise, it is unspecified
which waiting thread is unblocked. If the specified message queue is full and
\fBO_NONBLOCK\fR is set in the message queue description associated with
\fImqdes\fR, the message is not queued and \fBmq_send()\fR returns an error.
.sp
.LP
The \fBmq_timedsend()\fR function adds a message to the message queue specified
by \fImqdes\fR in the manner defined for the \fBmq_send()\fR function. However,
if the specified message queue is full and \fBO_NONBLOCK\fR is not set in the
message queue description associated with \fImqdes\fR, the wait for sufficient
room in the queue is terminated when the specified timeout expires. If
\fBO_NONBLOCK\fR is set in the message queue description, this function is
equivalent to \fBmq_send()\fR.
.sp
.LP
The \fBmq_reltimedsend_np()\fR function is identical to the
\fBmq_timedsend()\fR function, except that the timeout is specified as a
relative time interval.
.sp
.LP
For \fBmq_timedsend()\fR, the timeout expires when the absolute time specified
by \fIabs_timeout\fR passes, as measured by the \fBCLOCK_REALTIME\fR clock
(that is, when the value of that clock equals or exceeds \fIabs_timeout\fR), or
if the absolute time specified by \fIabs_timeout\fR has already been passed at
the time of the call.
.sp
.LP
For \fBmq_reltimedsend_np()\fR, the timeout expires when the time interval
specified by \fIrel_timeout\fR passes, as measured by the \fBCLOCK_REALTIME\fR
clock, or if the time interval specified by \fIrel_timeout\fR is negative at
the time of the call.
.sp
.LP
The resolution of the timeout is the resolution of the \fBCLOCK_REALTIME\fR
clock. The \fBtimespec\fR argument is defined in the <\fBtime.h\fR> header.
.sp
.LP
Under no circumstance does the operation fail with a timeout if there is
sufficient room in the queue to add the message immediately. The validity of
the timeout parameter need not be checked when there is sufficient room in the
queue.
.SH RETURN VALUES
.LP
Upon successful completion, \fBmq_send()\fR, \fBmq_timedsend()\fR, and
\fBmq_reltimedsend_np()\fR return \fB0\fR. Otherwise, no message is enqueued,
the functions return \fB\(mi1\fR, and \fBerrno\fR is set to indicate the error.
.SH ERRORS
.LP
The \fBmq_send()\fR, \fBmq_timedsend()\fR, and \fBmq_reltimedsend_np()\fR
functions will fail if:
.sp
.ne 2
.na
\fB\fBEAGAIN\fR \fR
.ad
.RS 13n
The  \fBO_NONBLOCK\fR flag is set in the message queue description associated
with \fImqdes\fR, and the specified message queue is full.
.RE

.sp
.ne 2
.na
\fB\fBEBADF\fR \fR
.ad
.RS 13n
The \fImqdes\fR argument is not a valid message queue descriptor open for
writing.
.RE

.sp
.ne 2
.na
\fB\fBEINTR\fR \fR
.ad
.RS 13n
A signal interrupted the function call.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 13n
The value of \fImsg_prio\fR was outside the valid range.
.RE

.sp
.ne 2
.na
\fB\fBEINVAL\fR\fR
.ad
.RS 13n
The process or thread would have blocked, and the timeout parameter specified a
nanoseconds field value less than zero or greater than or equal to 1,000
million.
.RE

.sp
.ne 2
.na
\fB\fBEMSGSIZE\fR \fR
.ad
.RS 13n
The specified message length, \fImsg_len\fR, exceeds the message size attribute
of the message queue.
.RE

.sp
.ne 2
.na
\fB\fBETIMEDOUT\fR\fR
.ad
.RS 13n
The \fBO_NONBLOCK\fR flag was not set when the message queue was opened, but
the timeout expired before the message could be added to the queue.
.RE

.SH ATTRIBUTES
.LP
See \fBattributes\fR(7) for descriptions of the following attributes:
.sp

.sp
.TS
box;
l | l
l | l .
ATTRIBUTE TYPE	ATTRIBUTE VALUE
_
Interface Stability	Committed
_
MT-Level	MT-Safe
_
Standard	See below.
.TE

.sp
.LP
For \fBmq_send()\fR and \fBmq_timedsend()\fR, see \fBstandards\fR(7).
.SH SEE ALSO
.LP
.BR mq_open (3C),
.BR mq_receive (3C),
.BR mq_setattr (3C),
.BR sysconf (3C),
.BR mqueue.h (3HEAD),
.BR attributes (7),
.BR standards (7)
